The sample test paper is available here http://www.birminghamgrammarschools.org ... stions.pdf
and it gives an idea of the expected format (not expected level of difficulty).
For the first time, there will be a separate answer paper with boxes to shade - the answers will not be written in the main paper.
Generally CEM tests have involved a variety of cloze formats, including multi-choice cloze (with options), word bank cloze and missing letters cloze.
It isn't possible to say exactly which format will be in the exam this year.
As for being MCQ, the Maths is not usually MCQ and, as you can see on the sample paper, the children may need to write in then shade in, the numbers...